The present invention relates to a fuel injection device for combustion engines, preferably Diesel engines, with at least one pilot valve by means of which a control piston is displaceable by a pressure medium in order to convey fuel through at least one line/channel toward a combustion chamber of the internal combustion engine.
For a reliable and clean mixture formation, internal combustion engines, Diesel engines in particular, require an injection process consisting of several individual injection actions. The injection processes are divided into pre-injection and main injection of the fuel quantity. FIG. 3 illustrates the injection process. First, triggered by a switching pulse of the engine control, a pilot or pre-injection occurs. After a time period t, the pilot or pre-injection is terminated by a cut-off pulse and after a time period t, the main injection of the fuel is started by a switching pulse. The main injection has a longer duration than the pre-injection stage. Also, significantly more fuel is injected during the main injection than during the pre-injection stage. Particularly for producing the pre-injection quantity, a control unit is employed which, however, requires a high-cost electronic control system and which shows energetic losses. Frequently, a damper is employed for producing the pre-injection fuel quantity. This damper, however, cannot be fully utilized in each step of the operation. The reason for this is that the response times of the control hydraulic are too long in the event of small injection quantities due to the design of the control elements and a small pre-injection quantity can, therefore, be produced only with the help of a significant control-technical structural design and expenditure.
Therefore, it is an object of the present invention to provide a fuel injection device of the aforementioned kind such that a small pre-injection quantity can be produced with the fuel injection device having a simple structural design and only requiring a small control-technical expenditure and design.